The 50 1.8 G is fairly limited stopped down even in the centre not to talk about the borders/corners where it visibly suffers from field curvature.

This became very obvious to me once I used the D800 50 1.8 G and D800E 85 1.8 G side by side in studio. Since I currently also have a D800E, my further tries with the 50 1.8 G on the D800E confirmed that it never allows to achieve the crisp appearence that the 85 1.8 G can deliver.